1. Field of the Invention
The present invention relates to an image display device, such as a liquid crystal display device. More specifically, the present invention relates to an image display device which performs turning-on control in each of a plurality of regions on the rear surface of a panel, such as a liquid crystal panel section.
2. Description of the Background Art
A liquid crystal panel (liquid crystal panel section) which is thin and lightweight is widely used for the display section of a television receiver. However, the liquid crystal which requires a fixed period of time to reach desired transmittance from the application of driving voltage cannot respond to a fast-changed moving image. To solve such a problem, proposed is a technique in which the backlight provided on the rear surface of the liquid crystal panel is divided into a plurality of regions to be controlled so as to be turned on and off in each of the regions (backlight scanning) according to the timing of top-to-bottom scanning on the liquid crystal panel performed based on a video signal.
More specifically, after the driving voltage corresponding to the video signal is applied to the liquid crystal, the backlight in the corresponding region is continuously turned off until the liquid crystal approaches the desired transmittance, and at the time of approaching the desired transmittance, the backlight is turned on, whereby such control is repeated in each frame of the video signal. Such control allows the liquid crystal not to display the video in the period until the liquid crystal approaches the desired transmittance. Therefore, the fast-changed moving image can be displayed with less blurring.
On the other hand, the light source used for the backlight provided on the rear surface of the liquid crystal panel changes its brightness according to temperature change and with time. In addition, in the backlight using the light source in a plurality of colors, the change of the balance between the colors varies color temperature at the time of displaying white color.
To solve these problems, in the backlight system, the liquid crystal display device, and the backlight adjusting method disclosed in Japanese Patent Application Laid-Open No. 2007-287422, when the light emitting units configuring the backlight are controlled to be sequentially turned on (or off), each of the light emitting units of the backlight is independently turned on to detect its light amount by the photosensor. Then, the light amount of each of the light emitting units is feedback-controlled according to the detection result of the each of the light emitting unit. Therefore, good white balance without color shift can be realized.
However, when the control in Japanese Patent Application Laid-Open No. 2007-287422 is performed, it is necessary to independently turn on each of the divided backlight units (corresponding to each of the light emitting units) to detect its light amount by the photosensor. That is, since it is necessary to independently turn on the backlight unit in each of the regions in non-overlapped manner, the light emission period of the backlight unit in the region cannot be increased over a fixed period of time, with the result that the average brightness (contrast) per time cannot be higher. In addition, when the light emission periods of the backlight unit in each of the regions and the backlight unit in the region adjacent thereto are controlled to overlapped with each other to improve video contrast, the light amount of the backlight unit in each of the regions is affected by the light amount of the backlight unit in the region adjacent thereto with the result that another problem occurs.
Further, when other than the actual video display period, a light amount detection period is provided so that in the period, the backlight units are controlled to be sequentially independently turned on to detect their light amounts by the photosensor, the light amount detection period becomes longer in the case that the number of divided backlight units is large, which gives an unfavorable influence on video display.